1. Field of the Invention
This invention relates to digital communication systems and more particularly to such systems where it is desired to protect the system from faulty stations connected into the loop.
2. Description of the Prior Art
Digital communication systems are now becoming popular and are being particularly explored for use in situations where the various stations connected to the loop share a close physical proximity to each other. A signal correction arrangement is shown in co-pending patent application of C. R. Baugh, Ser. No. 91,406, filed Nov. 5, 1979. In the Baugh application, where is hereby incorporated by reference, there is disclosed a closed loop digital system having a time decay element inserted into the loop for the purpose of reducing unwanted signals to essentially zero. While the Baugh arrangement serves its intended purpose it only reduces those signals which are not reinforced by the station interface circuit. Thus, in situations where the interface circuit is faulty the erroneous information is continually placed on the loop thereby degrading the communication capability of the system.
One characteristic of digital loops is that synchronism must be preserved. Therefore, it is not feasible to merely remove a faulty station from a loop but rather steps must be taken to insure continued synchronism of the loop. In a copending patent application of Baxter-Cummiskey, Ser. No. 62,425, filed July 31, 1979 which application is hereby incorporated by reference, there is disclosed an arrangement for controlling digital loop synchronism. The Baxter-Cummiskey application does not deal with the problem of fault isolation.
Thus, a problem exists in that it is desirable to remove faulty stations or interface circuits from a digital loop system and to do so as soon as possible after an error occurs and to do so without elaborate control circuitry and without central processor intervention and in a manner which preserves synchronism of the loop.